Such test benches are known, e.g., as engine or transmission test benches and support the research and development with the help of e.g., functional tests, endurance trials for the mechanical load test, as well as consumption, exhaust gas, noise, or climate examinations. The engine test benches hereby simulate the operation of the engine in a complete vehicle under different environmental or application conditions. In the test bench, the test specimen can be coupled to a load device, e.g., an asynchronous machine, a permanent magnet engine, a hydraulic dynamometer, or an eddy-current brake. The load device simulates the load, against which the engine must operate in real operation. Electric motors, which are used as load device, are often also referred to as dynamometers.
During operation, such dynamometers require a high-capacity cooling system to avoid overheating. It is important to note, thereby, that the dynamometers most completely accommodate and remove the power supplied by the test specimen.
A number of cooling methods are known, in the case of which provision is made on the primary side for fluid media, such as water or oil, and on the secondary side for air. Air-cooled dynamometers have the advantage that an expensive and complex fluid supply and processing is not necessary. However, the extremely high noise level, which is caused by the cooling blower, is disadvantageous in the case of the air-cooling.
Typically, such cooling blowers always run at full capacity to ensure a sufficient cooling of the dynamometer for every operating state and maximally specified air intake temperature. The noise level developing thereby can make work in the vicinity of the test bench more difficult. In addition, energy is wasted when the cooling blower operates at full capacity, even though a smaller cooling capacity would also be sufficient in the case of certain testing states.
A test bench is disclosed in Japanese Patent 2006-023244 to Kazuhisa, in which a dynamometer is cooled by a cooling blower, wherein the speed of the blower motor is changed as a function of the current, which is supplied to the dynamometer. However, due to the fact that the speed of the test specimen and, thus, also the speed or the load of the dynamometer, respectively, often varies during a test cycle, the current supplied to the dynamometer must inevitably change just as often, which, in turn, leads to changing blower speeds. The whistling noises of the blower motor resulting from this are also perceived by the test bench personnel as being unpleasant; in addition, the durability of the fan is reduced by the constant accelerating.
A load device, which can be cooled by a blower device, is disclosed in French Patent 2894091 A1 to Telma. The blower device is turned on when a temperature sensor, which is disposed in the inlet area of the coolant on the load device, detects an exceeding of a limit temperature.
The invention is based on the object of specifying a test bench, in which the above-described disadvantages of the state of the art can be avoided.